After many years have slipped by, the leaders of the Greeks,opposed by the Fates, and damaged by the war,build a horse of mountainous size, through Pallas's divine art,and weave planks of fir over its ribs:they pretend it's a votive offering: this rumour spreads.
'Pallas' refers to Pallas Athena (or Minerva, syncretism being what it is), goddess over, among other things, weaving and disciplined warfare, in this case referring to weaving, but is must be noted that weaving together a giant horse as part of a battle strategy is pretty much a love letter to her.
As for the votive offering, it was a common belief that major voyages generally required making an offering or a sacrifice to the gods to ensure safe passage (some stories suggest Agamemnon sacrificed either a goat or his daughter to appease Artemis so his army could reach Troy). The Greeks wanted the Trojans to believe they had left the horse as their offering to Athena to protect them on their way home. This is pretty much entirely new information from Virgil, the Odyssey only established that the horse was part of Odysseus' scheme to kill him some Trojans (although it is noteworthy we're missing large sections of the epic cycle today that may have included those details), and was expanded on further in Quintus of Smyrna's Posthomerica a few centuries later.